1. Field of the Invention
The present invention relates to a disc holding mechanism for positioning and holding an optical disc such as a compact disc (CD) or a digital versatile disc (DVD) on the surface of a disc tray.
2. Description of the Related Art
Recently, as a recording medium such as a CD-R/RW or a DVD-R/RW/RAM are widely used, label printers that can print image or character information prepared by a computer on the label side of end-user compacts discs or digital versatile discs are increasing in demand.
Such label printers are generally classified into two types, i.e., a heat transfer type and an inkjet type. In both cases, basically, four colors of inks, i.e., magenta, yellow, cyan and black inks are used to print images on the label surface of optical discs.
In printing images on the label surfaces of optical discs, in order to position the optical discs in place and to prevent printing misalignment, an optical disc to be subjected to printing should be fixedly held on the surface of a disc tray. In label printers in production lines for manufacturing CDs or DVDs, surface-suction-type label printers having an excellent mass production capacity are generally used. However, a suction mechanism using a vacuum pump should be provided in such label printers, consequently enlarging the size of the printers, which are not suitable to be used as label printers for home. Further, label printers of the type for fixedly holding the outer circumferential edge of optical discs may be used. However, non-circular optical discs referred to as non-standard discs such as discs having shapes in imitation of characters or card type discs having the size of business name cards, are recently appearing. With the holding mechanisms of the surface suction type or the type that fixedly hold the external diameter part of optical discs, an attachment for fixedly holding a disc should be replaced with another attachment that correspond to the external shapes of optical discs to be subjected to printing, and the setting of the mechanism should be changed whenever the attachment is replaced. Thus, there is a problem in that the work efficiency typically decreases.
In order to solve the above problems, a positioning mechanism (for example, see Patent Document 1) is proposed, in which the positioning mechanism is fitted into a disc hole of an optical disc to be received in an received part provided in a disc tray and that pressed against an inner wall of the disc hole in the radial outward direction to position the optical disc.
FIG. 27 shows a printing tray 200 disclosed in Patent Document 1 exemplified above, a receiving recess 201 for receiving a disc for printing is formed in the main body of the tray. A positioning mechanism 202 is arranged at the center of the recess.
As shown in FIG. 27, the positioning mechanism 202 includes a frame body 203 that is fitted into the disc hole of the disc and fixing means 204 that presses the inner wall of the disc hole provided in the frame body 203 in the radial outward direction.
The fixing means 204 is provided with resilient members 205 (for example, a coil spring). One end of the resilient members 205 is fixed to a corresponding attachment surface 206 of the frame body 203 and the other end thereof is attached and fixed to a corresponding pushing piece 207. The resilient members 205 are radially provided on a plurality of attachment surfaces 206 equally distributed at the circumferential surface of the frame body 203. The resilient members 205 always bias the pushing pieces 207 provided in the respective resilient members 205 in the radial outward direction along the guide parts 208.
The optical disc received in the printing tray 200 are pressed and positioned in the radial outward direction by the pushing pieces 207 that are biased by the biasing force of resilient members 205.
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2002-260304
However, in the construction of the positioning mechanism proposed in Patent Document 1, throughout the different states of the printing tray, the inner wall of the disc hole is always in a state pressed by the positioning mechanism. Thus, when the optical disc on which label printing has been finished is removed from the printing tray, there is a problem in that load is applied to the inner diameter part of the disc to warp the optical disc and to affect the label surface on which printing has just been performed. In particular, the heat transfer type label printers require sufficient time until a transferred print image is fixed. Thus, there is a problem in that an image that has just been transferred frequently peels off due to the warpage of the optical disc and the optical disc slips.
Further, the label printers are often provided in an optical disc processing apparatus into which an auto-exchanger mechanism is assembled for automatic exchange of optical discs in consideration of the mass production capacity. However, the positioning mechanism proposed in Patent Document 1 is fixedly arranged at the center of a receiving recess of the printing tray and is always in a state fitted into the disc hole. Thus, there is a difficult of attaching or detaching an optical disc by means of machines. It is considered that the optical disc is attached or detached with the outer diameter part of the disc gripped. As described above, however, the positioning mechanism always presses the inner wall of the disc hole. Thus, there is a problem in that the load at the time of attaching or detaching the optical disc to or from the positioning mechanism is usually large and that it is difficult to cope with a non-circular optical disc.
Moreover, in order to prevent an erroneous operation of the label printer, there is a need to precisely determine whether or not any optical disc exists on the disc tray.